Themes of the Day:

• Limestones & Dolostones

Limestones & Dolostones

• Sea-Level Curves
• Overview of Carbonates
  • Carbonates - (CO₃)^2- - 10-15% of all sed rocks
  • Acid reaction - CaCO₃+2HCl=Ca²⁺+2Cl^-+CO₂+H₂O
  • often quite pure - only minor clays, silica as impurities - Why? Think: depositional environments
• Textures - more important for classification because of minimal chemical variability
  • chunky
  • laminated
  • lumpy
• Grain Types (allochemical particles)
  • Fossils
  • Ooids, pisoliths (concentric), oncolites (radiating)
  • Oncoliths
  • Peloids - nice stylolites, too!
  • Limeclasts
• Matrix
  • micritic
  • sparry
  • microspar
• Grain Size, Sorting, Rounding
• Insoluble Residues - chert nodules
• Classification
  • Dunham
  • Folk
  • Naming Examples
• Structures
  • Current-generated - cephalopods
  • Geopetal - gastropods
  • Lamination - fenestrae, stromatolites
• Depositional Environments
  • Modern Day Reefs - Late Cretaceous
  • Modern Day Reef - Andros Island, Bahamas - Corals
  • Platform & Shelf - Lower Ordovician, USA
  • Micritic Mud Mounds
  • Organic Reefs - Upper Devonian, Ellesmere Island
  • Deep Ocean - Laytonville Limestone, CA
  • Lacustrine
• CaCO₃ Equilibria
  • CaCO₃+CO₂+H₂O=Ca²⁺+2H⁺+2CO₃^2-
  • Temperature effect - CO₂ solubility is key
  • Shaken, not stirred - soda/beer/champagne
  • Salinity - lessens CO₂ solubility
  • Organic activity - photosynthesis (plants) vs. respiration (animals)
  • Soil Zone
• Diagenesis
  • Early Cementation - hardgrounds
  • Strandline
  • Meteoritic Water
  • Later Diagenesis
  • Compaction - Mechanical and Chemical
  • Stylolites - thin section, slab, outcrop
  • Burial Cementation - polarized light vs. cathodoluminescence
  • Secondary Porosity - Vugs - Calcite solubility
• Dolostones
  • Field Observations - Limestone/Dolostone contact, Lost Burro Fm.
  • Where are all the modern ones? - Sea level vs. Dolostone abundance through the Phanerozoic
  • Lab Studies
  • Textures - thin section 1, thin section 2 (cathodoluminescence), thin section 3 (ooid replacement)
• Dolostone Environments of Formation
  • Evaporative Reflux - Guadalupe Mts., TX/NM
  • Mixing of Saline and Fresh Waters - Jamaica
• Geochemistry of Dolomite - CaMg(CO₃)₂